This proposal in the area of behavioral geriatrics deals with health behavior and aging. We propose to investigate a theoretical model of the determinants of illness behavior (symptom perception and medical care utilization) for older adults in an HMO, a medical care setting of increasing importance for the Medicare Program. This model has implications for promoting health behaviors and reducing inappropriate use of medical services. One major hypothesis is that discontinuities in older adults' lives, loss of family members, economic insecurity, and pre-existing poor health increase symptom perception and physician utilization. A second hypothesis is that inactivity, time spent alone, and boredom also increase illness behavior. Third, these determinants are mediated by diffuse attention to inner feelings, and inappropriate coping behavior which isolates older adults from social support resources and interferes with life activities. Finally, the model suggests that age, gender, and chronic morbidity affect the illness behavior of older adults. A prospective study is proposed which will follow three cohorts aged 55-64, 65-74, and 75 and older for one year. A total of 450 older adults will be recruited from the Rutgers Community Health Plan, an HMO which is actively enrolling older adults. Respondents will be interviewed twice, one year apart, with a fixed interview protocol. In addition, open-ended probes will explore in depth how illness behavior, discontinuities, activity levels, and coping behavior are associated. Utilization and illness data will be obtained from HMO records for the year between interviews, and linked with perceptions of health and other key variables in our model. Both cross-sectional and prospective data will be analyzed with multivariate structural equation methods. If this model is substantiated, it will help identify groups of older adults most likely to use medical care inappropriately and suggest alternatives to medical care that promote functioning of older adults and help contain medical care costs.